1. Field of the Invention
The present invention relates to an exposure apparatus for exposing the pattern of a mask on a substrate by using an exposure light. More particularly, the invention relates to an exposure apparatus suitably used for correction of a difference of pattern line widths between masks during picture synthesis carried out using a plurality of masks.
This application is based on Japanese Patent Application No. Hei 11-286102, the contents of which are incorporated herein by reference.
2. Description of the Background Art
As regards a display device for a personal computer, a television set or the like, in recent years, a liquid crystal display substrate which enables a display to make thin, has frequently been used. The liquid crystal display substrate of such a kind is manufactured by using a photolithography method patterning a desired shaped transparent thin-film electrode on a glass plate rectangular in shape viewed from the above. As such a photolithography apparatus, a projection type exposure apparatus is used, which is designed to expose an exposure pattern formed on the mask onto a photoresist layer on the glass plate through a projection optical system.
FIG. 11 shows an example of the exposure apparatus of the above kind. This exposure apparatus denoted by 1 is based on a so-called step and repeat system. According to this system, a pattern formed on a reticle R (e.g., reticle RA) is exposed onto a predetermined region of a glass plate (simply referred to as a plate, hereinafter) 4 held on a stage 3, and then the plate 4 steps by a given distance and the exposure of the reticle R pattern (e.g., reticle RB) is repeated. The pattern on the reticle R, illuminated by an illumination optical system (not shown), is image-formed on the plate 4 held on the stage 3 through a projection optical system 5. The stage 3 is controlled for its position based on accurate monitoring of a position coordinate by laser interferometers 6a and 6b for measuring positions in X and Y directions respectively. Orthogonal coordinate systems X and Y on the stage 3 are used as reference frame for the exposure apparatus 1.
For the purpose of exposing an image of a pattern (geometrical pattern by a light transmitting portion and a light shielding portion) formed on the reticle R onto the plate 4 coated with a resist layer having a specified thickness (1 to 5 xcexcm), the exposure apparatus 1 comprises an illumination optical system provided to project an exposure light having almost constant intensity with a uniform illumiance distribution from above the reticle R for predetermined time. Alternatively, the exposure apparatus 1 comprises an illumination optical system provided to project a plurality of exposure lights (pulse light) from the pulse emission type laser light source, until its integrated quantity of light reaches a predetermined amount. In either case, to control a line width of the pattern formed on the resist layer with sufficient accuracy, the exposure apparatus 1 is controlled to print the pattern image of the reticle R onto the resist layer with optimal exposure energy, i.e., an optimal energy quantity.
Accordingly, the stage 3 is provided with a sensor (not shown) for measuring the irradiation quantity of an exposure light, which makes it possible to measure the quantity of an illumination light which transmitted from the illumination optical system through the reticle R and the projection optical system 5 and forming an image on the stage 3. The quantity of an illumination light P (mW/cm2) on the stage 3 is measured beforehand, and exposure time t (msec; t=J/P) for exposing the pattern on the reticle R is calculated based on the illumination light quantity P and an optimal exposure energy quantity J (mJ/cm2) decided from the resist and the process. During actual exposure, the exposure time t is adjusted by controlling the illumination optical system (e.g., a shutter). In other words, exposure applied to the plate 4 is controlled by controlling such exposure time. Regarding a focus during exposure, control is performed such that the plate 4 can always be set at the best focus of the projection optical system 5 by using an AF sensor (not shown) to measure the height position of the plate 4 and driving the stage 3 in an optical axial direction.
In addition, in the exposure apparatus 1, in order to find the optimal energy quantity of the exposure light projected to the plate 4, the plate 4 is developed after the execution of test exposure therefor, the line width of a linear pattern is measured by an optical microsope or a dedicated line width measuring device, and then comparison is made with a designed line width value. Alternatively, an optimal exposure condition is decided based on the fact that a line width becomes smallest under a given condition.
For example, if development is carried out after a light width pattern as a part of patterns to be exposed on the reticle R is exposed onto the plate 4 based on the step and repeat system while increasing exposure (exposure time) little by little, a resist image is left according to the pattern on the reticle R. However, because the exposure varies little by little, in the case of a positive resist, as shown in FIG. 12, the line width pattern 7 of the resist image becomes narrow corresponding to the exposure (exposure time). Generally, to plot the change of the line width corresponding to the exposure energy and the focus, a substantially linear change is made like that shown in FIG. 13 if a change in the exposure energy is very small. Thus, based on such a relationship, by reversibly calculating exposure such that gives an optimal line width with respect to a given pattern or process, and performing correction control to expose by this exposure, the line width accuracy of a transferred pattern can be enhanced.
However, the following problems are inherent in the foregoing conventional exposure apparatus.
For example, with the progress in the screen enlargement of the liquid crystal display device, the size of the plate used for the exposure apparatus has been increased more and more. As an exposure method for such a large plate, a so-called picture synthesis method has been used. As shown in FIG. 11, this picture synthesis method uses a plurality of reticles RAto RD respectively corresponding to each of the divided LCD patterns, exposes the pattern of one reticle on the exposure region of the glass substrate corresponding to the reticle, then makes the plate to step and changes the reticle to another, exposes the pattern of the selected reticle on an exposure region corresponding to this reticle, and thus forms an LCD pattern synthesizing a plurality of patterns on the plate.
For example, in the case of exposure on the plate 4 having panels P1 and P2 arranged, panels being made by stitching divided patterns Ato D like those shown in FIG. 14, exposure is carried out while changing each of the reticles RA to RD having the divided patterns A to D to another by a reticle replacement mechanism 8, and the large panels P1 and P2 are formed by stitching the divided patterns A to D as shown in FIG. 11.
On the other hand, as it is in recent years, the pattern has been scaled down more with such a screen enlargement, creating the necessity of considering even line width accuracy caused by a reticle manufacturing error. For a layer (a gate layer or a drain/source layer) to be strictly managed practically, optimal light exposure is calculated based on the result of test exposure, and is fed back to exposure control data. Such an operation is carried out to prevent the damaging of device characteristics caused by a level difference, which occurs by presence of a line difference between the stitched portions of the patterns, and a reduction in device quality caused by discontinuous changes in a lamination error at the exposure regions of the respective layers and a pattern line width difference, which occur in the stitched portions of the patterns when picture synthesized divided patterns are laminated to form a multilayer structure.
However, if there are a plurality of reticles constituting a certain layer, as described above, enormous time and labor must be expended to obtain optimal light exposure by carrying out test light exposure for all the reticles. Consequently, a reduction inevitably occurs in production efficiency.
The present invention was made with the foregoing problems in mind, and it is an object of the invention to provide an exposure apparatus capable of easily performing exposure on a substrate such as a plate or the like without any line width differences between patterns on the substrate even if the exposure on the substrate is executed by using a plurality of reticles (or masks).
In a first aspect of the invention, the exposure apparatus is designed to expose a plurality of patterns stitched together through a projection optical system onto a substrate by an exposure light. The exposure apparatus comprises: a line width detector that detects a pattern line width; and a control unit that controls a light quantity of the exposure light based on a detection result of the line width detector.
In a second aspect of the invention, a photoelectric sensor is used as the line width detector.
In a third aspect of the invention, the photoelectric sensor is a charge coupled device.
In a fourth aspect of the invention, the line width detector comprises: an illumination unit that illuminates a detection light toward the patterns; a light receiving unit that receives the detection light through the patterns and the projection optical system; and a computing unit that computes the pattern line width based on a light quantity of the detection light received by the light receiving unit.
In a fifth aspect of the invention, the detection light obtains the pattern line width based on a change in light quantity intercepted by the patterns when the detection light and the patterns perform a relative movement.
In a sixth aspect of the invention, the pattern line width is obtained based on relative positions of the relative movement and the change in light quantity.
In a seventh aspect of the invention, a direction of the relative movement is a direction approximately perpendicular to the patterns.
In an eighth aspect of the invention, the exposure apparatus further comprises a substrate stage that holds and moves the substrate, wherein the illumination unit is provided in the substrate stage.
In a ninth aspect of the invention, the control unit controls the light exposure based on a difference among the respective pattern line widths when the plurality of patterns are stitched together on the substrate.
In a tenth aspect of the invention, the line width detector detects the pattern line width in the vicinity of stitched portion.
Thus, according to the exposure apparatus of the invention, even if a plurality of masks are used, the pattern line widths can be detected by the line width detector, and the light exposure of the exposure light can be controlled by the control unit to prevent the difference of pattern line widths from the detected line widths when exposure is carried out on the substrate. Hence, even if there is a pattern width difference among the masks, exposure can be carried out on the substrate such that no difference occurs between the line widths printed, without executing test exposure. In addition, when the pattern line widths exposed on the substrate are managed based on absolute values, test exposure is carried out for one mask selected from the plurality of masks, a relative relation is calculated among the pattern line width on the selected mask, the light exposure of the exposure light and the pattern line width printed on the substrate. For the other masks, pattern line widths printed on the substrate can be obtained based on the calculated relative relation and the detected line widths.